chill

n.

Old English ciele, cele "cold, coolness, chill, frost," from Proto-Germanic *kal- "to be cold," from PIE root *gel- "cold" (see cold). According to OED, the word seems to have been obsolete after c.1400 (displaced by cold) and the modern use is a back-formation since c.1600 from the verb.

Sheila E. sizzles in the new flick, Krush Groove, but some New York critics couldn't groove with it because many of the terms are unfamiliar to them. Examples: breakin' out (slang for leaving), chill (for cool down) and death (for something that's really good). ["Jet," Nov. 11, 1985]

chill out

To not get so excited; to take it easy: “Hey, chill out, we'll get there sooner or later.” This phrase can also mean to relax; to have a good time: “On my vacation I just want to chill out on the beach with a good book.” It is often shortened to the imperative chill: “Chill! We can do without your bad behavior.”